The present invention relates to improvements in moveable load-carrying assemblies and refers particularly, but not exclusively to a steerable, movable, load-carrying assembly. The present invention also includes a centralising mechanism for use with such load-carrying assemblies to assist in steering of the overall assembly.
Throughout this specification reference will be made to a perambulator, pusher or push-chair for babies, invalids and the like. It should be understood that such preferred embodiments are given by way of example only and the invention is not to be considered to be limited to such usage. Indeed, the present invention will be suitable for use in any assembly intended to be propelled by human effort rather than motive power including, for example, trolleys, carts, shopping trolleys, wheel barrows, strollers, toy prams, trailers, caravans, boat trailers, wheeled jacks for vehicles, wheel chairs, gurnies, hospital beds, hospital stretchers mounted on a wheeled base, work platforms, library trolleys, and other similar articles having a number of wheels and/or castors.
Throughout this specification, reference to a wheel or wheels is to be taken as including a reference to a castor or castors, or a wheel acting as a castor.
Furthermore, throughout this specification reference to a chassis is to be taken as including reference to a framework.
In accordance with the known prior art, perambulators normally have fixed wheels. This gives rise to undue and undesirable hardship in their use. For example, the turning circle of fixed wheel perambulators can be rather large, with obvious limitations and consequences. Also, there can be scrubbing of the wheels when turning thus increasing wear.
In accordance with the prior art, moveable assemblies of the aforementioned type can be said to be one of three forms:
(i) a first where all four wheels are fixed and not in any way steerable (for example, traditional forms of perambulators);
(ii) a second (for example, child strollers and the like) having the rear wheels fixed, whilst the front wheels are swivellable; or
(iii) a third where all four wheels are separately swivellable (for example, supermarket trolleys).
In practice it has been found that each of the three forms exhibit a number of advantages which make them suited to certain uses, but suffer from disadvantages which limit their suitability for all uses.
When all four wheels are fixed (the first form), one advantage is that the wheels can be quite large in diameter, thus allowing the assembly to more easily traverse uneven terrain. Another advantage is that such assemblies are suitable for use along pathways where the operator does not need to concentrate on manoeuvring the assembly in normal travel and only has to do so when a change of direction is required. Therefore, when larger diameter wheels are used with fixed wheel assemblies, the ride is smoother for the occupant, an important result when the occupant may be a baby. It has also been found that fixed wheel assemblies may traverse a slope or undulating ground without there being excessive exertion by the operator to keep the assembly in the desired direction other than when a change in direction is required.
Such fixed wheel assemblies suffer from the disadvantage that it is difficult to change direction. Two commonly used methods are to either push down on the handle to lift the front wheels off the ground and to pivot the handle horizontally to point the assembly in the desired new direction of travel; or to lift the handle so that the rear wheels leave the ground and to pivot the handle horizontally to achieve the desired new direction of travel. Both of these alternatives can require the application of significant effort and skill.
Further disadvantages of such fixed wheel assemblies include the excessive wear and tear on the frame component of the overall structure, which can result in the frame being bent or distorted. Furthermore, the effort required by the operator may be excessive. As a result, assemblies of the fixed wheel type have been found to be unsuited for use as articles such as shopping trolleys, where frequent changes in direction are required and normally within a small area.
For the second form of assembly is that with fixed rear wheels and swivellable front wheels. Such assemblies have the advantages of being more easily manoeuvrable, in terms of both space and effort. However, this form has the disadvantage that it is necessary to utilise small-diameter wheels to enable the caster-style swivel action to allow the front wheels to rotate through 360 degrees as they are generally mounted or have to swivel under the assembly. The use of such smaller diameter wheels make it more difficult for the assembly to traverse rough or uneven surfaces, and also gives a far less comfortable ride to the occupant when compared with larger-diameter fixed wheeled assemblies. Furthermore, the swivellable front wheels are normally casters, or operate as caster wheels. In consequence they are not linked together and individually follow the terrain which can result in the swivellable front wheels facing in different directions, making it extremely difficult for the operator to maintain control, especially when the assembly is traversing a sloping surface. With such assemblies, when traversing a cambered or sloping surface it is necessary for the operator to maintain concentration and expend a significant effort to keep the assembly heading in the desired direction.
Assemblies with four separately swivellable wheelsxe2x80x94the third formxe2x80x94have the advantages of being: very manoeuvrable; able to turn within their own length; and able to be used equally well and efficiently when pushed and/or pulled in either direction. Such assemblies have therefore being found to be specially suited for use as shopping trolleys, baby strollers and the like.
Such assemblies also exhibit a number of disadvantages. Firstly, such assemblies are best suited for use on horizontal, flat surfaces, with it being difficult to maintain control when moving such an assembly across a slope. Furthermore, as all wheels have to be able to rotate through 360 degrees, assemblies of this form can only be produced with smaller diameter wheels, once again giving rise to a less comfortable ride for the occupant even if the wheels are locked in the forward position, thereby allowing forward movement only. As all four swivel wheels are caster wheel sets, all may operate independently, especially when uneven surfaces are being traversed. As the wheels are not linked they can all be pointing in different directions at any given time. The assembly may therefore be difficult to control.
With known load-carrying assemblies there is a tendency for the direction of movement to be readily upset. A variety of means have been employed in an attempt to give improved steerability, but without success. The present invention seeks to overcome the problems and disadvantages of the prior art by providing a mechanism to retain steerable wheels of a steerable assembly in a position allowing for straight-forward motion, and which acts to return the steerable wheels to the position which corresponds to straight motion for the assembly. Preferably this is regardless of the extent to which the steerable wheels may be caused to shift due to variations in terrain, etc.
In a further aspect, the present invention preferably acts to prevent any tendency the assembly might exhibit to drift out of the position which corresponds to straight ahead motion and compensate for the tendency of the assembly to steer in anything other than a straight line.
There has been very little development of steering systems for load-carrying assemblies of the present invention. For example PCT/GB96/00687 discloses a trolley, such as a supermarket trolley, having a castor at each corner. The castors are arranged as a driving (rear) castor and as a driven (front) castor. A worm gear arrangement allows the driving castor on one side to drive the driven castor on that side such that when the driving castor turns in one direction, the driven castor turns in the opposite direction. However, there is no linkage of the castors from one side to the other. Therefore, the castors on one side could be turned to the right (rear) and left (front), and the castors on the other side could be turned to the left (rear) and right (front). This would defeat the entire exercise. Also it is only relevant for castors located immediately below the frame and is not useable for any other form of wheel, nor for any other form of product.
Furthermore, U.S. Pat. Nos. 4,348,033 and 4,405,140 relate to a steerable bob sled where the four runners of the sled are linked to enable them to be steered. However, the mechanism involved is a complex arrangement requiring numerous parts, with the use of cables and links. Furthermore, it is intended to controlled from within rather than without. This is a fundamental difference in that when controlled from within there is an occupant who can steer the apparatus and it is not intended to be steered by external forces. With a device such as a perambulator or child stroller, it is steered from without and is therefore intended inherently to be controlled by external forces. Furthermore, with devices such as perambulators and strollers, it is inherently intended that they not be controlled by internal forces otherwise a wriggling child or baby could control the direction of the perambulator or stroller, and this is totally contrary to what is required.
In accordance with a first aspect of the present invention there is provided a moveable load-carrying assembly including a chassis having a plurality of wheels arranged as a first wheel set and a second wheel set, each wheel being rotatable and swivellable relative to the chassis; the wheels of the first wheel set being connected by a first linkage, and the wheels of the second wheel set being connected by a second linkage; and wherein one of the wheels of the second wheel set is linked to the opposite one of the wheels of the first wheel set by a link such that when one of the wheels of the first wheel set is swivelled in one direction relative to the chassis, all the wheels of the first wheel set swivel in that direction in unison and all the wheels of the second wheel set swivel in the opposite direction in unison.
Preferably, there are two wheels in the front wheel set. More preferably, there are two wheels in the rear wheel set. Advantageously, the chassis has a front transverse member and a rear transverse member. More advantageously, the front transverse member is the front linkage. Furthermore, the rear transverse member may be the rear linkage.
Preferably, the link is a bar or rod pivotally attached to one of the front wheels and to the diagonally opposite one of the rear wheels.
In accordance with a further aspect of the present invention there is provided a moveable load-carrying assembly wherein means are included to provide three distinct modes of operation for the rear set of wheels, the modes corresponding to straight-line travel (either forward or in reverse), folly-steerable travel (again either forward or in reverse), and a braking mode.
In accordance with another aspect of the present invention there is provided an apparatus for controlling the direction of travel of a steerable assembly, the apparatus including:
(i) a first member associated with a tie-rod operably connected to one or more steerable wheels of the assembly;
(ii) at least one further member associated with a fixed chassis member of the assembly, the at least one further member being selectively and continuously pivotably moveable relative to the fixed chassis member between respective inoperative and operative end positions; and
(iii) resilient means associated with the at least one further member, the arrangement being such that, in use, when the steerable wheels of said assembly undergo a change in direction, the first member and the at least one further member come into contact, whereby the resilient means acts to return the at least one further member to its inoperative position, thereby correcting the steering of said assembly.